The present invention is generally directed to circuit monitoring devices, and more particularly, to an improved remote-indicating fault indicator.
Various types of fault indicators have been constructed for detecting electrical faults in power distribution systems, including clamp-on type fault indicators, which clamp over a cable of the system and derive their operating power from the magnetic field surrounding the cable, and test-point mounted type fault indicator, which attach to test point sockets provided on connectors or other system components and derive their operating power by means of a capacitive coupling to the monitored conductor. In addition, either type of fault indicator may be either self-resetting, wherein the fault indication is automatically reset following resumption of current flow in the conductor, or manually reset, wherein an operator must manually clear a fault indication.
A particularly advantageous construction is shown in U.S. Pat. No. 5,070,301 of the present inventor, wherein high impedance liquid crystal displays are utilized in conjunction with a novel capacitive charge transfer circuit to provide an "F" indication following a fault, and an "N" indication during the presence of a normal current.
It is sometimes desirable to provide an indication or signal of fault occurrence and/or power restoration at a location remote from the fault indicator, as where a large number of circuits are monitored at a central control center, or where switching is to be controlled or inhibited in accordance with circuit status.
The present invention enables a preferred liquid crystal display type fault indicator to supply these remote indications with a minimum number of additional components and without the use of electromechanical relays or switch devices.
Accordingly, it is a general object of the present invention to provide a new and improved remote-indicating fault indicator.
It is a more specific object of the invention to provide a remote-indicating fault indicator which is more compact and easier to manufacture.
It is a still more specific object of the invention to provide a solid-state fault indicator which provides both fault and line powered circuit status indications at a remote location.
A fault indicator for signaling at a remote location the occurrence of a fault current in a monitored electrical conductor includes a housing, a high impedance optical shutter device having a pair of control electrodes disposed in operative association with a layer of voltage-responsive light controlling material, the optical shutter having a first light transmissivity condition in the absence of an actuating signal applied to the control electrodes, and a second light transmissivity in the presence of an actuating signal applied to the control electrodes. First circuit means including a voltage source apply an actuating signal to the control electrodes following occurrence of a fault current in the monitored conductor to condition the optical shutter device to the second light transmissivity condition. A light source directs a beam of light through the optical shutter device. A light detector receives the beam of light after transmission through the optical shutter device and produces an output dependent on the amplitude of the incident light; and second circuit means responsive to the output of the light detector produce an output signal indicative of the occurrence of a fault.